In the industry of manufacturing continuous sheets, such as webs of tissue paper or similar, for example to produce rolls of toilet paper, paper napkins, rolls of kitchen towels and similar, machines are used to emboss the cellulose web material, by means of which the originally smooth material is subjected to a permanent deformation resulting in the formation of embossed protrusions. Two or more plies of web material are usually embossed separately from one another and then bonded, using glue, with different mutual arrangements of the protrusions produced by embossing on the two or more plies. Generally speaking, the embossed plies are bonded using so-called tip-to-tip technology, or using a so-called nested technology, or using variants of these two base technologies.
In tip-to-tip technology, two embossed plies are bonded by bringing the protrusions of one ply into contact with the protrusions of the other ply. The two plies are glued by means of glue applied to the protrusion heads.
With nested technology, on the other hand, protrusions formed on one ply nest in the free spaces between the protrusions produced on the other ply. Glue is applied to the protrusions of one of the two plies to bond the two plies together.
In some cases more than two plies are bonded together, for example two outer embossed plies and one intermediate ply, which may be smooth or embossed as well.
To produce embossed plies bonded using tip-to-tip technology or nested technology, different machine and/or embossing rollers need to be used, specifically designed to allow bonding using one technique or the other.
For instance, U.S. Pat. No. 5,736,223 discloses an embossing device comprising a first embossing roller, a second embossing roller and a third embossing roller. Said embossing rollers co-act with respective first pressure roller, second pressure roller and third pressure roller. The arrangement is configured to manufacture a three-ply web, namely two external plies and in intermediate, internal ply. The two external plies are arranged and bonded to one another in a tip-to-tip configuration, while the intermediate ply is bonded in a nested configuration with one of the two external plies.
EP-A-2095935 discloses an embossing device comprising a double tip-to-tip embossing arrangement. Four embossing rollers and four pressure rollers are combined such as to emboss and laminate four plies to one another. This known embossing device is not suitable to manufacture nested plies.
Paper converting industries often require flexible machines, i.e. machines that can switch from the production of embossed plies using tip-to-tip technology, to the production of embossed plies using nested technology, and vice-versa, with the possibility of switching from one type of operation to the other quickly so as to meet constantly changing market needs, even for small batches.
There is therefore a need to provide embossing devices that are capable of producing multi-ply web material using one or other of the production techniques, and that can switch quickly and with a high degree of flexibility, by means of simple, easily-automated operations, from the production of one type of embossed material to the production of another type of embossed material.